It is indispensable to use herbicides to protect important crop plants such as rice, wheat, corn, soybean, cotton and sugar beet from weeds and thereby to increase the harvest. Especially in recent years, a selective herbicide is desired which is capable of selectively killing weeds without showing any phytotoxicity against crop plants when applied to the foliages of crop plants and weeds simultaneously in a field where such useful crop plants and weeds are coexistent. Further, with a view to avoiding environmental pollution and reducing the costs for transportation and application, researches and developments have been conducted for many years for compounds having high herbicidal effects at low doses. Some of the compounds having such properties are presently used as selective herbicides. However, there still exists a need for better new compounds having such properties.
As the prior art showing a chemical structure similar to that of the compounds of the present invention, Japanese Unexamined Patent Publications No. 15962/1983, No. 103371/1983, No. 126859/1983, No. 48973/1985, No. 214785/1985, No. 134377/1986, No. 151577/1989, No. 45473/1990, No. 91060/1990, No. 7284/1991 and No. 68562/1991, and U.S. Pat. Nos. 4,559,081, 4,592,776, 4,602,939, 4,622,065, 4,666,508, 4,696,695 and 4,741,762, disclose compounds having sulfonylurea bonded to a nitrogen atom. However, compounds having sulfonylurea bonded to a nitrogen atom of an imino structure like the compounds of the present invention have not been known at all, and they are novel compounds.